Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$166.74	13.831%	$189.8018	$189.80	$189.80	$189.80
Purchase #2	$126.79	6.388%	$134.8893	$134.89	$134.90	$134.90
Purchase #3	$200.51	10.871%	$222.3074	$222.31	$222.30	$222.30
Purchase #4	$74.47	10.209%	$82.0726	$82.07	$82.05	$82.10
Purchase #5	$164.42	8.133%	$177.7923	$177.79	$177.80	$177.80
Purchase #6	$57.92	5.663%	$61.2	$61.20	$61.20	$61.20
Purchase #7	$155.38	7.301%	$166.7243	$166.72	$166.70	$166.70
7 purchase totals =	$946.23		$1,034.7877	$1,034.78	$1,034.75	$1,034.80